The present invention relates to the field of treatment of defective human knee joints, and in particular, to replacement and repair of defective or damaged human knee joint soft tissue using a substantially immunologically compatible soft tissue from a non-human animal.
The term xe2x80x9csoft tissuexe2x80x9d, as used herein, refers to cartilaginous structures, such as meniscus and articular cartilage; ligaments, such as anterior cruciate ligaments; tendons; and heart valves.
Meniscus Cartilage
Specifically, the femoral condyles articulate with the surface plateaus of the tibia, through the cartilaginous medial and lateral menisci soft tissue, and all of these structures are held in place by various ligaments. The medial and lateral menisci are structures comprised of cells called fibrochondrocytes and an extracellular matrix of collagen and elastic fibers as well as a variety of proteoglycans. Undamaged menisci provide shock absorption for the knee by ensuring proper force distribution, stabilization, and lubrication for the interacting bone surfaces within the knee joint, which are routinely exposed to repeated compression loading during normal activity. Much of the shock absorbing function on the medial and lateral menisci is derived from the elastic properties inherent to cartilage. When menisci are damaged through injury, disease, or inflammation, arthritic changes occur in the knee joint, with consequent loss of function.
Since joint cartilage in adults does not naturally regenerate to a significant degree once it is destroyed, damaged adult menisci have historically been treated by a variety of surgical interventions. Damaged menisci have been removed and replaced with prosthetic devices. An artificial knee joint having a rigid plastic femoral member and a metal tibial member is disclosed in U.S. Pat. No. 4,034,418. A number of meniscus prostheses have been devised which employ resilient materials such as silicone rubber or natural rubber, as in U.S. Pat. No. 4,344,193 and U.S. Pat. No. 4,502,161. Additional deformable, flexible resilient materials for a meniscus prosthesis such as collagen, tendon, or fibrocartilage are disclosed in U.S. Pat. No. 5,092,894 and U.S. Pat. No. 5,171,322. A cartilage replacement apparatus constructed of polyethylene plastic filled with small ball bearings or gelatinous fluid is described in U.S. Pat. No. 5,358,525. However, the known artificial prostheses have been unsatisfactory for treatment of damaged menisci, since they are deficient in the elastic, and therefore in the shock-absorbing, properties characteristic of natural menisci. Moreover, the known artificial devices have not proven able to withstand the force inherent to routine knee joint function.
One of the present inventors provided improved prosthetic menisci in several of his earlier patents (U.S. Pat. No. 4,880,429; U.S. Pat. No. 5,007,934; U.S. Pat. No. 5,116,374; and U.S. Pat. No. 5,158,574). These patents generally disclose prosthetic menisci formulated from dry, porous matrices of processed natural fibers such as reconstituted cross-linked collagen, which optionally include glycosaminoglycan molecules. Generally, the source of collagen for these prosthetic menisci has been animal Achilles tendons or skin. The reconstitution process removes non-collagenous materials such as glycoproteins, proteoglycans, lipids, native glycosaminoglycans, and the like, which may confer additional elastic properties to the original tissue.
Articular Cartilage
Articular cartilage soft tissue covers the ends of all bones that form articulating joints in humans and animals. Articular cartilage is made of fibrochondrocytes and an extracellular matrix of collagen fibers as well as a variety of proteoglycans. The cartilage acts in the joint as a mechanism for force distribution and as a lubricant in the area of contact between the bones. Without articular cartilage, stress concentration and friction would occur to the degree that the joint would not permit ease of motion. Loss of the articular cartilage usually leads to painful arthritis and decreased joint motion.
Damaged adult articular cartilage has historically been treated by a variety of surgical interventions including repair, replacement, or by excision. With repair or excision, regeneration of tissue may occur, although the tissue is usually temporary and inadequate to withstand the normal joint forces.
Replacement of articular cartilage usually has been by allografting (Sengupta et al. (1974) J. Bone Suro. 56B(l):167-177; Rodrigo et al. (1978) Clin Orth. 134:342-349) by periosteal grafts (see, e.g., Engkvist (1979) Scan J. Plast. Reconstr. Suro. 13:361-369; Rubak (1982) Acta Orthop. Scan. 53:181-186) or with metal and/or plastic components (Rubash et al., eds. (1991) Clin. Orth. Rel. Res. 271:2-96). Allografting dead cartilage tissue has been tried for years with minimal success. This approach has been only partially successful over the long term due to the host""s immunologic response to the graft, failures in the cryopreservation process, and failures of the attachment sites. Replacement of an entire joint surface with metal and plastic components has met excellent success for the older, more sedentary patients, but is generally considered insufficient for tolerating the impact of athletic activities, and has not been shown to restore normal joint mechanics.
In alternative prior art approaches, articular cartilage has been replaced with prostheses composed of bone and/or artificial materials. For example, U.S. Pat. No. 4,627,853 describes the use of demineralized allogenic or xenogeneic bone segments as replacements. The proper functioning of these replacements depends on the differential demineralization of the bone segments. U.S. Pat. No. 4,846,835 describes a grafting technique for transplantation of fibrochondrocytes to promote healing lesions in articular cartilage. U.S. Pat. No. 4,642,120 describes the use of gel-like compositions containing embryonal fibrochondrocytes. U.S. Pat. No. 5,306,311 describes a prosthetic articular cartilage which includes a dry, porous volume matrix adapted to have in vivo an outer contour sustantially the same as that of natural articular cartilage.
Despite these developments, the replacement of articular cartilage soft tissue with structures consisting of permanent artificial materials generally has been less than satisfactory, and a structure suitable as articular cartilage and constructed from natural resorbable materials, or analogs thereof, has not been developed. Because the opposing articular cartilage of mammalian joints is so fragile, it will not withstand abrasive interfaces nor compliance variances from normal which eventually result from the implantation of prior art artificial cartilage. Additionally, joint forces are multiples of body weight which, in the case of the knee and hip, are typically encountered over a million cycles per year. Thus far, prior art permanent artificial cartilages have not been composed of materials having natural articular cartilage properties, nor have they been able to be positioned securely enough to withstand such routine forces.
Ligaments
Anterior cruciate ligament soft tissue of the knee (hereinafter the ACL) functions to resist anterior displacement of the tibia from the femur at all flexion positions. The ACL also resists hyperextension and contributes to rotational stability of the fully extended knee during internal and external tibial rotation. The ACL may play a role in proprioception. The ACL is made up of connective tissue structures composed of cells, water, collagen, proteoglycans, fibronectin, elastin, and other glycoproteins. Cyril Frank, M.D. et al., Normal Ligament: Structure, Function, and Composition. Injury and Repair of the Musculoskeletal Soft Tissues, 2:45-101. Structurally, the ACL attaches to a depression in the front of the intercondyloid eminence of the tibia extending postero-superiorly to the medial wall of the lateral femoral condyle.
The preferred treatment of damaged ACL is ligament reconstruction, using a bone-ligament-bone autograft. Cruciate ligament reconstruction has the advantage of immediate stability and a potential for immediate vigorous rehabilitation. However, the disadvantages to ACL reconstruction are significant: for example, normal anatomy is disrupted when the patellar tendon or hamstring tendons are used for the reconstruction; placement of intraarticular hardware is required for ligament fixation; anterior knee pain frequently occurs. Moreover, recent reviews of cruciate ligament reconstruction indicate an increased risk of degenerative arthritis with intraarticular ACL reconstruction in large groups of patients.
A second method of treating ACL injuries, referred to as xe2x80x9cprimary repairxe2x80x9d, involves suturing the torn structure back into place. Primary ACL repair has the potential advantages of a limited arthroscopic approach, minimal disruption of normal anatomy, and an out-patient procedure under a local anesthetic. The potential disadvantage of primary cruciate ligament repair is the perception that over the long term ACL repairs do not provide stability in a sufficient number of patients, and that subsequent reconstruction may be required at a later date. The success rate of anterior cruciate ligament repair has generally hovered in the 60% to 70% range.
Heart Valves
Heart valves are composed of fibrochondrocytes and an extracellular matrix of collagen and elastic fibers, as well as a variety of proteoglycans. Various synthetic and tissue based materials (the latter either from the recipient organism or from a different organism within the same species) have been used for forming heart valve replacements. Each have their advantages and disadvantages.
In the case of synthetic heart valves, it may be possible to modify advantageously the properties of the heart valves by altering the monomers and/or the reaction conditions of the synthetic polymers. Synthetic heart valves may be associated with thromboembolism and mechanical failure, however. See U.S. Pat. No. 4,755,593.
Tissue based heart valves may demonstrate superior blood contacting properties relative to their synthetic counterparts. Tissue based heart valves also may be associated with inferior in vivo stability, however. See U.S. Pat. No. 4,755,593.
Pericardial xenograft tissue valves have been introduced as alternatives to the synthetic and the tissue based valves described above. See Ionescu, M. I. et al., Heart Valve Replacement With The Ionescu-Shiley Pericardial Xenograft, J. Thorac. Cardiovas. Surg. 73; 31-42 (1977). Such valves may continue to have calcification and durability problems, however. See Morse, D, ed. Guide To Prosthetic Heart Valves, Springer-Verlag, New York, 225-232 (1985).
Accordingly, there is a need for mechanically durable, flexible heart valves replacements which are capable of contacting the blood and are stable in vivo.
Xenografts
Much of the structure and many of the properties of original soft tissues may be retained in transplants through use of heterograft or xenograft materials, that is, soft tissue from a different species than the graft recipient. For example, tendons or ligaments from cows or other animals are covered with a synthetic mesh and transplanted into a heterologous host in U.S. Pat. No. 4,400,833. Flat tissues such as pig pericardia are also disclosed as being suitable for heterologous transplantation in U.S. Pat. No. 4,400,833. Bovine peritoneum fabricated into a biomaterial suitable for prosthetic heart valves, vascular grafts, burn and other wound dressings is disclosed in U.S. Pat. No. 4,755,593. Bovine, ovine, or porcine blood vessel xenografts are disclosed in WO 84/03036. However, none of these disclosures describe the use of a xenograft for soft tissue replacement.
Once implanted in an individual, a xenograft provokes immunogenic reactions such as chronic and hyperacute rejection of the xenograft. The term xe2x80x9cchronic rejectionxe2x80x9d, as used herein refers to an immunological reaction in an individual against a xenograft being implanted into the individual. Typically, chronic rejection is mediated by the interaction of IgG natural antibodies in the serum of the individual receiving the xenograft and carbohydrate moieties expressed on cells, and/or cellular matrices and/or extracellular components of the xenograft. For example, transplantation of soft tissue cartilage xenografts from nonprimate mammals (e.g., porcine or bovine origin) into humans is primarily prevented by the interaction between the IgG natural anti-Gal antibody present in the serum of humans with the carbohydrate structure Galxcex11-3Galxcex21--4G1cNAc-R (a-galactosyl or xcex1-gal epitope) expressed in the xenograft. K. R. Stone et al., Porcine and bovine cartilage transplants in cynomolgus monkey: I. A model for chronic xenograft rejection, 63 Transplantation 640-645 (1997); U. Galili et al., Porcine and bovine cartilage transplants in cynomolgus monkey: II. Changes in anti-Gal response during chronic rejection, 63 Transplantation 646-651 (1997). In chronic rejection, the immune system typically responds within one to two weeks of implantation of the xenograft.
In contrast with xe2x80x9cchronic rejectionxe2x80x9d, xe2x80x9chyper acute rejectionxe2x80x9d as used herein, refers to the immunological reaction in an individual against a xenograft being implanted into the individual, where the rejection is typically mediated by the interaction of IgM natural antibodies in the serum of the individual receiving the xenograft and carbohydrate moieties expressed on cells. This interaction activates the complement system causing lysis of the vascular bed and stoppage of blood flow in the receiving individual within minutes to two to three hours.
The term xe2x80x9cextracellular componentsxe2x80x9d, as used herein, refers to any extracellular water, collagen and elastic fibers, proteoglycans, fibronectin, elastin, and other glycoproteins, which are present in soft tissue.
Xenograft materials may be chemically treated to reduce immunogenicity prior to implantation into a recipient. For example, glutaraldehyde is used to cross-link or xe2x80x9ctan xe2x80x9d xenograft tissue in order to reduce its antigenicity, as described in detail in U.S. Pat. No. 4,755,593. Other agents such as aliphatic and aromatic diamine compounds may provide additional crosslinking through the side chain carboxyl groups of aspartic and glutamic acid residues of the collagen polypeptide. Glutaraldehyde and diamine tanning also increases the stability of the xenograft tissue.
Xenograft tissues may also be subjected to various physical treatments in preparation for implantation. For example, U.S. Pat. No. 4,755,593 discloses subjecting xenograft tissue to mechanical strain by stretching to produce a thinner and stiffer biomaterial for grafting. Tissue for allograft transplantation is commonly cryopreserved to optimize cell viability during storage, as disclosed, for example, in U.S. Pat. No. 5,071,741; U.S. Pat. No. 5,131,850; U.S. Pat. No. 5,160,313; and U.S. Pat. No. 5,171,660. U.S. Pat. No. 5,071,741 discloses that freezing tissues causes mechanical injuries to cells therein because of extracellular or intracellular ice crystal formation and osmotic dehydration.
The present invention provides a substantially non-immunogenic soft tissue xenograft for implantation into a human in need of soft tissue repair or replacement. The invention further provides methods for processing xenogeneic soft tissue with reduced immunogenicity but with substantially native elasticity and load-bearing capabilities for xenografting into humans.
As used herein, the term xe2x80x9cxenograftxe2x80x9d is synonymous with the term xe2x80x9cheterograftxe2x80x9d and refers to a graft transferred from an animal of one species to one of another species. Stedman ""s Medical Dictionary, Williams and Wilkins, Baltimore, Md. (1995).
As used herein, the term xe2x80x9cxenogeneicxe2x80x9d, as in, for example, xenogeneic soft tissue, refers to soft tissue transferred from an animal of one species to one of another species. Id.
The methods of the invention, include, alone or in combination, treatment with radiation, one or more cycles of freezing and thawing, treatment with a chemical cross-linking agent, treatment with alcohol or ozonation. In addition to or in lieu of these methods, the methods of the invention include, alone or in combination, in any order, a cellular disruption treatment, glycosidase digestion of carbohydrate moieties of the xenograft, or treatment with proteoglycan-depleting factors. Optionally, the glycosidase digestion or proteoglycan-depleting factor treatment can be followed by further treatments, such as, for example, treatment of carbohydrate moieties of the xenograft with capping molecules. After one or more of the above-described processing steps, the methods of the invention provide a xenograft having substantially the same mechanical properties as a native soft tissue.
As used herein, the term xe2x80x9ccellular disruptionxe2x80x9d as in, for example, cellular disruption treatment, refers to a treatment for killing cells.
As used herein, the term xe2x80x9ccapping molecule(s)xe2x80x9d, refers to molecule(s) which link with carbohydrate chains such that the xenograft is no longer recognized as foreign by the subject""s immune system.
As used herein, the terms xe2x80x9cto capxe2x80x9d or xe2x80x9ccappingxe2x80x9d, refer to linking a capping molecule such as a carbohydrate unit to the end of a carbohydrate chain, as in, for example, covalently linking a carbohydrate unit to surface carbohydrate moieties on the xenograft.
In one embodiment, the invention provides an article of manufacture comprising a substantially non-immunogenic soft tissue xenograft for implantation into a human.
In another embodiment, the invention provides a method of preparing a soft tissue xenograft for implantation into a human, which includes removing at least a portion of a soft tissue from a non-human animal to provide a xenograft; washing the xenograft in water and alcohol; and subjecting the xenograft to at least one treatment selected from the group consisting of exposure to ultraviolet radiation, immersion in alcohol, ozonation, and freeze/thaw cycling, whereby the xenograft has substantially the same mechanical properties as a corresponding portion of a native soft tissue.
As used herein, the term xe2x80x9cportionxe2x80x9d, as in, for example, a portion of soft tissue, second surface carbohydrate moieties or proteoglycans, refers to all or less than all of the respective soft tissue, second surface carbohydrate moieties or proteoglycans of the xenograft.
In another embodiment, the invention provides a method of preparing a soft tissue xenograft for implantation into a human, which includes removing at least a portion of a soft tissue from a non-human animal to provide a xenograft; washing the xenograft in water and alcohol; subjecting the xenograft to a cellular disruption treatment; and digesting the xenograft with a glycosidase to remove first surface carbohydrate moieties, whereby the xenograft has substantially the same properties as a corresponding portion of a native soft tissue.
As used herein, the term xe2x80x9cfirst surface carbohydrate moiety (moieties)xe2x80x9d refers to a terminal xcex1-galactosyl sugar at the non-reducing end of a carbohydrate chain.
In still other embodiments, this method can include additional steps such as, for example, treating second surface carbohydrate moieties on the xenograft with capping molecules to cap at least a portion of the second surface carbohydrate moieties, whereby the xenograft is substantially non-immunogenic.
As used herein, the term xe2x80x9csecond surface carbohydrate moiety (moieties)xe2x80x9d refers to a N-acetyllactosamine residue at the non-reducing end of a carbohydrate chain, the residue being non-capped either naturally or as a result of prior cleavage of an xcex1-galactosyl epitope.
In a further embodiment, the invention provides a method of preparing a soft tissue xenograft for implantation into a human, which includes removing at least a portion of soft tissue from a non-human animal to provide a xenograft; washing the xenograft in water and alcohol; subjecting the xenograft to a cellular disruption treatment; and digesting the xenograft with a proteoglycan-depleting factor to remove at least a portion of the proteoglycans from the xenograft, whereby the xenograft has substantially the same mechanical properties as a corresponding portion of a native soft tissue and is substantially non-immunogenic.
In yet further embodiments, the invention provides articles of manufacture including substantially non-immunogenic soft tissue xenografts for implantation into humans produced by one or more of the above-identified methods of the invention.
In another embodiment, the invention provides a soft tissue xenograft for implantation into a human which includes a portion of a soft tissue from a non-human animal, wherein the portion has substantially no surface carbohydrate moieties which are susceptible to glycosidase digestion, and whereby the portion has substantially the same mechanical properties as a corresponding portion of a native soft tissue.
In yet another embodiment, the invention provides a soft tissue xenograft for implantation into a human which includes a portion of a soft tissue from a non-human animal, wherein the portion includes extracellular components and substantially only dead cells, the extracellular components and dead cells having substantially no surface xcex1-galactosyl moieties and having capping molecules linked to at least a portion of surface carbohydrate moieties. The portion of the soft tissue is substantially non-immunogenic and has substantially the same mechanical properties as the native soft tissue.
In still yet another embodiment, the invention provides a soft tissue xenograft for implantation into a human which includes a portion of a soft tissue from a non-human animal, wherein the portion includes extracellular components and substantially only dead cells, the extracellular components having reduced proteoglycans. The portion of the soft tissue is substantially non-immunogenic and has substantially the same mechanical properties as the native soft tissue.